Power Distribution
Definition
Large lighting rigs are usually supplied in three-phase, which spreads the load over three line conductors. IEC 60038 lists 230/400 V as the standard low-voltage system in Europe and many other countries, meaning 230 volts between a phase and neutral and 400 volts between phases. In North America, 120/208 V systems are common for entertainment power. With balanced linear loads, the neutral carries only the imbalance between the three phases, so fixtures are spread roughly evenly across L1, L2 and L3. When the whole load sits on one phase, that phase's breaker trips while the other two remain lightly loaded.
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The guide
LED drivers, switch-mode power supplies and phase-control dimmers are non-linear loads. Their third-order (triplen) harmonics add in the neutral instead of cancelling, so the neutral current can equal or exceed the phase current even when the phases are balanced, up to about 1.73 times in theory. IEC 60364-5-52 takes harmonics into account in conductor sizing. Temporary installations are covered by IEC 60364-7-711 (part 7-711 of NF C 15-100 in France), by BS 7909 in the United Kingdom and by NEC Article 520 in the United States.
The feeder carries the full current from the supply to the distribution. It is rated for the load, and its connections are secure and correctly terminated, because a loose high-current connection heats up and can start a fire. The sequence is fixed: calculate the load, distribute it across the phases, confirm that cables and protective devices are rated for it, then energise. Phase rotation also matters for three-phase motors and some distribution equipment, because it sets the direction in which motors turn.
The rule
The load is calculated and balanced across the phases before anything is powered.
Glossary terms
Sources
- IEC 60038:2009 : tensions normalisées, dont 230/400 V (50 Hz) et 120/208 V (60 Hz) · webstore.iec.ch
- IEC 60038 (Wikipédia, pointeur secondaire) : notation phase-neutre/phase-phase des réseaux triphasés · en.wikipedia.org
- Power Monitors Inc., Understanding Triplen Harmonics : harmoniques de rang 3 additionnés dans le neutre, jusqu'à 1,73 fois le courant de phase · library.powermonitors.com
- ELEK Software : dimensionnement du neutre en présence d'harmoniques (IEC 60364-5-52) · elek.com
- IEC 60364-7-711:2026 (NF C 15-100 partie 7-711) : installations électriques temporaires d'expositions et de spectacles ; remplace l'édition 2018 · webstore.iec.ch
- BS 7909:2023+A1:2024 : installations électriques temporaires pour le spectacle (Royaume-Uni) · knowledge.bsigroup.com
- Schneider Electric, Electrical Installation Guide, dimensionnement du neutre : courant de neutre jusqu'à environ 1,73 fois le courant de phase avec des harmoniques de rang 3 · electrical-installation.org
- NFPA 70 (NEC), article 520 : théâtres, lieux de spectacle et zones similaires · up.codes